Trouble Draining the Boiler

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Jah1010

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Hi all,

I bought this house recently and am still learning the systems. I have a 2 zone, oil-fueled hydronic heat system, and the circulator pump just broke (or rather, is breaking). I have a new one and am ready to install it. My plan was to drain the system from the drain valve (bottom circle in image), replace the pump, fill from the main fill line (middle circle), close the valve between the fill and the upper drain valve (top of picture, red handle), and bleed any air out of there until clean water comes out.




Unfortunately, I never quite got there. I opened up the bottom drain valve and only a little water came out. I opened the top one as well, thinking there was a vacuum, and only a little more came out - about 1/3 of a gallon total, with both valves open. There aren't any other bleeder valves in the system other than the automatic one above the expansion tank, so I'm not sure what else to do. (FYI, system was at 12 psi when I started this, though it loses pressure often. That's another thread though.)

I know I have substantial air in the system, which was a problem I was hoping to solve during this process too, but I backed out of the job. I realized also that the bottom drain valve needs to be replaced (it will only turn using channel locks), and with snow in the forecast, both of these unforeseen hiccups made me close the valves, fill the boiler, and fire it up again for now.

Any thoughts on why so little water came out? I don't mind calling a plumber, but I also would give this another try in a week or two when cold weather isn't so threatening.

Thanks!
 

Dana

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Why are you going do drain the system just to replace the pump? That would only add more air to the system, which is the opposite of what you want. What you want to do isolate as the pump as much as possible with the valves, then once the pump is replaced, open only the valves necessary to fill the portion of the system that lost water.

The black handled gate valve in the middle appears to be on a system bypass branch (?) to keep the entering water temperature at the boiler high enough to avoid condensation issues in the boiler & flue. If it has been operated only partly open the wear of the flow is probably enough to keep it from sealing tightly.

The blue & yellow handled ball valves would probably isolate most of the system from the boiler when close (can't see the full plumbing configuration to know for sure), The black handled gate valve directly above the pump probably needs to be closed to isolate the system from the boiler.

If there is a huge slug of corrosion sludge plugging the drain port valve below the pump, that could make it sticky & hard to turn, and may be a hint as to what destroyed the pump. With all of the valves in their normal operation positions you might try back-pressuring with a hose from the potable water, then crack open the red handled gated valve then open the drain port below the pump to see it if reverse flow can blow out any plugs. Be sure to not overpressurize the system when performing that operation.

When the heating system is over it's probably worth doing a more thorough flushing of the system to clear any built up sludge, but for now you want to just clear out the worst of it and keep the system running. Most systems can go years, even a decade or more without needing a major flush, but systems with a lot of older cast iron radiation may be better served with an annual flush.
 

Dana

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Upon closer inspection it looks like the blue handled ball valve isolates the output of the pressure relief valve on the boiler, in which case it should NEVER be closed when the boiler is operating.

A more frontal picture of the near boiler plumbing from a bit further back might make it easier to see what is connected to what.
 
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